1. Technical Field
The technical field relates to an imaging apparatus such as a digital still camera, and a lens barrel mountable to the imaging apparatus.
2. Related Art
JP-A-6-153049 discloses an autofocus apparatus capable of performing zoom tracking in response to a manual zoom operation performed by a user. The autofocus apparatus stores in advance a plurality of zoom tracking curves. The autofocus apparatus can control the position of a zoom lens in a stepwise manner. Moreover, the autofocus apparatus determines a position to which the zoom lens is moved, based on a manual zoom operation performed by the user. The autofocus apparatus then selects one zoom tracking curve based on information about the determined position to which the zoom lens is moved. It is noted that the zoom tracking is an operation to keep a focus even if zoom operation is done after the autofocus apparatus comes into focus by moving the focus lens.
In this manner, the autofocus apparatus can prevent an erroneous selection of the zoom tracking curve, particularly resulting in rapid focus control upon zooming operation.
However, the autofocus apparatus described in JP-A-6-153049 can be applied only to a zoom tracking operation in which the zoom lens is electrically driven by a power zoom, and does not support a zoom tracking operation in when the user manually operates the zoom lens.
Generally, in a zoom tracking operation, when a zoom magnification is changed in a focus state, a focus lens or correction lens is driven according to a zoom tracking curve to keep the focus state. At that time, a control target position of the focus lens or correction lens is determined based on the current position of the zoom lens, along the zoom tracking curve. In cases where the focus lens or correction lens is driven based on the current position of the zoom lens, the zoom lens has already moved to another position and thus a focus state cannot be obtained when the focus lens or correction lens reaches the control target position. Hence, it is necessary to determine a control target position of the focus lens or correction lens by also taking into account the moving speed of the zoom lens.
Specifically, in the case of a power zoom in which the zoom lens is driven by a motor, the zoom speed is constant and thus a control target position of the focus lens or correction lens is determined by adding a constant value based on the zoom speed. In this case, a determination of a control target position is easy. However, in the case of manually performing a zoom operation by the user, the speed of turning a zoom ring by the user is not constant. Therefore, a determination of the control target position of the focus lens or correction lens is not easy.